The invention relates to an integrated circuit, for operation in an area with ionizing radiation.
The invention further relates to a hazard alarm for operation in an area with ionizing radiation.
Finally the invention relates to a method for determining information about damage to an integrated circuit caused by ionizing radiation impacting thereon.
An integrated circuit (also called IC for short) is an electronic circuit accommodated on a semiconductor substrate or on a semiconductor chip. It is consequently also called a solid-state circuit or a monolithic circuit.
An integrated circuit of this type typically has a plurality of electronic components wired to one another. The semiconductor material from which the integrated circuit is manufactured is preferably silicon. Alternatively it can be a germanium, gallium arsenide, silicon carbide or other suitable semiconductor material. Preferably a CMOS (Complementary Metal Oxide Semiconductor) semiconductor process is used for the technical implementation of the semiconductor components of the integrated circuit. Alternatively use can also be made of a PMOS or NMOS semiconductor process, a bipolar semiconductor process or a combination thereof, e.g. a BiCMOS semiconductor process.
The hazard alarms are e.g. fire alarms, e.g. optical smoke detectors or heat detectors. Optical smoke detectors can be based e.g. on the scattered light principle or on the opto-acoustic principle. If the hazard alarm is a heat detector, the temperature currently prevailing in the vicinity of the heat detector is detected, e.g. by a temperature-dependent resistor. The hazard alarms in question can also be smoke gas detectors, which have a gas sensor as a detector unit, e.g. a gas FET (Field Effect Transistor). Furthermore, the hazard alarms can be motion detectors which have a PIR (Passive Infrared) detector unit for motion detection. The hazard alarms in question can also comprise combinations of the aforementioned detector units.
The hazard alarm can also be designed as a linear smoke detector which is based on the extinction principle. Such linear smoke detectors are in particular used in large or narrow spaces, for example in corridors, warehouses and fabrication halls and in aircraft hangars, and are mounted underneath the ceiling on the walls. In a first embodiment transmitter and receiver are opposite one another, and no reflector is necessary. In a second embodiment the light beam emitted by the transmitter is deflected via a reflector back to a receiver. Transmitter and receiver are disposed adjacent to one another. The measured distance of such linear smoke detectors is typically in the range between 20 m and 200 m, which in the case of the first embodiment corresponds to a distance between transmitter and receiver corresponding to the measured distance. In the second embodiment the distance between transmitter/receiver and the reflector corresponds to half the measured distance.
Ionizing radiation means particle radiation or electromagnetic radiation with ionizing energies of 5 eV and more which is able to eject electrons from atoms or molecules so that positively charged ions or molecular residues are left behind.
Much ionizing radiation arises from radioactive substances, e.g. in an area with increased, in particular with high radioactive radiation. Such areas can be e.g. a nuclear area or outer space. Nuclear areas in particular refer to spatially delimited areas for example inside a nuclear power plant, a nuclear recycling facility or a final or intermediate place of storage for radioactive waste.
Ionizing or radioactive radiation generally has a destructive damaging effect on electronic components and in particular on semiconductor components. Such components have very fine semiconductor structures of less than 1 μm, in particular of less than 100 nm. All types of high-energy ionizing radiation interact in this case with a semiconductor crystal. While it is possible to shield against alpha and beta radiation, as particle radiation, using materials just a few millimeters thick, e.g. a housing plate or a plastic housing, effective shielding against electromagnetic gamma radiation is possible only by the use of large amounts of material. Depending on the shielding required, lead shields with a shielding thickness of a meter and more may be required. Even though shielding against alpha and beta radiation is possible comparatively simply, the effect of the gamma radiation on the shielding or on the housing of the semiconductor components nevertheless means that to a minor extent secondary alpha and beta particles are also created, which in turn interact with the semiconductor crystal. The interaction of such an irradiated particle with a lattice atom means that the latter can be released from the lattice, and a void is created. The free atom can, if it possesses sufficient transferred impact energy, eject further atoms, or migrate to an interstitial position. What is known as a vacancy-interstitial complex is formed.
A major effect of impacting radiation is the generation of crystal defects, which give rise to additional energy states inside the forbidden band and thus generate centers of recombination. These effects occur in accelerated form in the case of semiconductor microstructures with an increased level of complexity, e.g. in microcontrollers, microprocessors, ASICs or FPGAs. In contrast, resistors or capacitors are scarcely effected.
For this reason use is preferably made of robust discrete semiconductor components such as transistors or diodes, in order to take account of an accelerated degeneration of the electrical parameters in the circuit, especially since overwhelmingly radiation-hard, older integrated semiconductor components, e.g. ICs, logic gates, etc., which have a structure size of more than 1 μm, are scarcely available on the semiconductor market any longer as a result of far-advanced miniaturization.
By using discrete semiconductor components a minimum service life, e.g. of 3 years, depending on the relevant requirements, e.g. those in a nuclear power plant, can thus be achieved. A requirement of this type may e.g. be that a fire alarm must “withstand” a radiation dose or an energy dose of 0.25 Gy in 3-year period. Gy (Gray, =100 rad) here designates the SI unit of absorbed energy dose D. The time-related absorbed energy dose is here referred to as the dose rate or dose output.
A full description of the effect of radioactive radiation on electronic semiconductor components, in particular the damage cumulated over time or temporary damage associated therewith to such semiconductor components, is provided in the dissertation “Bauelemente-Degradation durch radioaktive Strahlung and deren Konsequenzen für den Entwurf strahlenresistenter elektronischer Schaltungen” [Component degradation as a result of radioactive radiation and its consequences for the design of radiation-resistant electronic circuits] by Detlef Brumbi, Faculty for Electronic Engineering at the Ruhr University Bochum, 1990.
Publication JPL D-33339 by the Jet Propulsion Laboratory (JPL) of the California Institute of Technology (CIT), Pasadena, Calif., USA, dated Jun. 6, 2009, entitled “Test Method for Enhanced Low Dose Rate Damage (ELDRS) Effects in Integrated Circuits for Outer Planetary Mission” examined, with a view to the planned Jupiter Europa Orbiter (JEO) mission, a range of integrated circuits such as voltage regulators, operational amplifiers and comparators using bipolar and BiCMOS technology for their sensitivity to radiation using a two-stage accelerated test procedure. To speed up the test, higher dose rates were used compared to the real dose rates expected during the mission. A real test with the cumulated radiation dose expected for the entire mission of up to 1000 krad(Si) would in contrast take too much time and hence would be impracticable. In the proposed ELDRS test the circuits are first irradiated with a low maximum dose rate of 10 mrad(Si)/s up to a radiation dose of 30 to 50 krad. The circuits are then irradiated with a dose rate of 40 mrad(Si) until the required overall radiation dose is reached.
Appendix 1 to the publication also discloses that during the irradiation test the temperature of the circuits can also be increased in addition to increasing the dose rate, in order to offset the increase in the rate of formation of induced hole sites caused thereby by an increase in a countervailing recombination rate due to thermal causes. It is also disclosed that if the circuit temperature selected is too high (“If the temperature is too high, the damage may actually anneal, as shown in the second figure for the Motorola LM324”), as in the example in FIGS. 10 and 11 at 135° C., the damage to the circuit actually to be determined undesirably disappears again as a result of the “annealing effect”.